Shift trailing whitespace outside of inline mdast nodes

[danburzo]

For example, this HTML:

<span style="font-weight: 400;">Select the </span><strong>Project Window </strong><span style="font-weight: 400;">in your Dashboard.</span>

Produces this Markdown:

Select the __Project Window __in your Dashboard.

Add a mdast-level util to shift the trailing whitespace to the outside of inline (emphasis) nodes.

[danburzo]

A basic implementation, based on ideas in this discussion:

/*
	Remark plugin to fix trailing whitespace in inline nodes.
	See: https://github.com/orgs/syntax-tree/discussions/60
*/
function remarkTrailingWhitespace() {
	return function (tree, file) {
		visit(tree, ['strong', 'emphasis'], (node, index, parent) => {
			// Remove empty nodes
			if (!node.children.length) {
				parent.children.splice(index, 1);
				return SKIP;
			}

			const first = node.children[0];

			// Remove image nodes from within emphasis nodes
			if (first.type === 'image') {
				parent.children.splice(index, 1, first);
				return SKIP;
			}

			// Remove trailing whitespace at the beginning
			if (first.type === 'text') {
				const start_match = first.value.match(/^(\s+)(.*)/);
				if (start_match) {
					const [_, start_ws, start_text] = start_match;
					parent.children.splice(index, 0, {
						type: 'text',
						value: start_ws
					});
					if (start_text) {
						// has non-whitespace content
						first.value = start_text;
					} else {
						// all-whitespace content
						node.children.shift();
					}
					// Re-visit this node
					return [SKIP, index - 1];
				}
			}

			const last = node.children[node.children.length - 1];
			if (last.type === 'text') {
				const end_match = last.value.match(/(.*?)(\s+)$/);
				if (end_match) {
					const [_, end_text, end_ws] = end_match;
					parent.children.splice(index + 1, 0, {
						type: 'text',
						value: end_ws
					});
					if (end_text) {
						last.value = end_text;
					} else {
						node.children.pop();
					}
				}
			}

			return SKIP;
		});
	};
}